Timing escapement mechanism



Feb. 9, 1965 D. POPOVITCH 3,168,833

TIMING ESCAPEMENT MECHANISM Filed Sept. 26, 1963 2 Sheets-Sheet 1 Fig.

TO TIMED MECHANlSM AND ENERGY SOURCE as? 32 Fig 2 INVENTOR. DRAGOLYOUB POPOVITCH BY/V 14,0 g 5Z3 00 M 9 X M ATTORNEY5.

1965 D. POPOVITCH 3,168,833

TIMING ESCAPEMENT MECHANISM Filed Sept. 26, 1963 2 Sheets-Sheet 2 AXE: OF SPIN 7 v F Tlh dER I5 I GEAR AND TRAN ENERGY |9 SOURCE Fig.6

AKlS OF SPIN INVENTOR- DRAGOLYOUB POPOVITC l2--- BY M.

flap/5 L l WQM ATTORNEY5.

United States Patent 3,163,833 TIMING ESCAPEMENT MEHANESM Dragolyoub Popovitch, Denviiie, N.J., assignor to the The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

The present invention relates to mechanical timers or clocks of the type usedto provide control functions according to elapsed time while a moving body, such as a high-speed aircraft, missile, or artillery shell, travels between two points in its flight path or trajectory. Such timers are thus subjected to the same forces as the moving bodies or flight vehicles in which they are mounted or by which they are carried. These forces may result from rapidacceleration or set-back, rapid directional changes,' high-speed rotation or spin, and the like, and by reason of definite adverse effects on the moving parts thereof,

functioning in some cases. If the moving body isa modern timed artillery shell, for example, the centrifugal forces developed inside the timer by the spinning action of the shell will thus affect all moving parts and the accuracyof its time setting or measurement.

In conventional timers of the above type, it has been found that the most affected of the moving parts are the necessary timer source of energy which is generally a wound main spring,the actual time-measuring assembly which is generally a timing escapement mechanism, and a connecting reduction gear trainl between the energy source and the said escapementrnechanism. It has also been found, however, that the adverse effects of these forces on the energy-sources, such as the wound driving spring, and onvthe gear trains, can readily be compensated or eliminated by proper design. In modern timers of this type, the escapement assembly or mechanism remains as having the moving parts most affected by the forces acting on the moving body by which it is carried.

The present invention, therefore, relates more particularly to timing escapement assemblies or mechanisms for mechanical timers and clocks of the type described, and has for its primary object to provide an improved timing escapement mechanism which may be regulated in frequency in relatively small increments, and which, is extremely stable and accurate in its timing functions under a wide range of different externally-applied forces.

It is also an object of this invention to provide an'im-' proved and simplified timing escapement mechanism which meets extreme spin and setback or acceleration conditions in connection with the timing of fuzes for modern high-speed artillery shells andlikeprojectiles in.

1 can affect the accuracy of the timer and even stop its flhdfi i atented Feb. 9, i965 GS, with no efiective frequency or timing change in the escapement mechanism and no effective shortening or lengthening of the functioning time of the timer with respect to the setting time selected.

Since the escapement or escapement mechanism, of any timer or clock of the type referred to, regulates its beat frequency or functioning time with respect to a selected setting time, its operation must be substantially independent of the forces applied to the moving body or flight vehicle in which the timer or clock is mounted, it useful timing results are to be obtained. Heretofore with artillery shells for example, the most accurate fuze function, at the set times, occurred only when the spin rates were those at which the fuze, that is, its escapement mechanism or timer, was regulated. Existing artillery shell fuzes with conventional timers and escapement mechanisms tend to function longer than the set time if used at spin rates lower-than the regulated spin rate. Conversely. such shell fuzes tend to function shorter than the set time whennsed' at spin rates higher than the regulated spin rate.

With a timing escapement mechanism,embodying the invention, applied to a timer for a mechanical time fuze of modern design, accurate functioning about the set time can be achieved over a spin range from 2,000 to 24,000 r.p.rn., for example. This achievement is made possible by the timing escapement mechanism of the present invention and certain features thereof as here considered.

The escapement assembly or mechanism, in accordance with the invention, is of the type having a rotary escapement wheel and a pivoted escapement lever with oscillating masses and two-bladed escapementmeans or pallets,

arranged in balanced'relation about the pivot axis of an 7 operating arbor, in a generally conventional manner, to' control the step-by-step rotary movement of the escapement wheel. The latter is connected through a gear train with .the controlled mechanism and the driving spring or Y other energy source for the escapement mechanism and "known structures of this type.

connected with the arbor to vibrate as the arbor oscillates in response to the mass movement about the axis of the arbor. Timing rate or frequency regulation is provided by means of a movable clamp connected with the spring to determine its active length at the inner end. The spring may be a single blade or a double blade, and in one or two radial positions, as will hereinafter be described.

In accordance with the invention, a substantially spininsensitive escapement mechanism is achieved by the improved construction above described. The escapement spring is reduced in length and positioned relatively close to the spin axis at its operating or vibrating end. The

total mass of the working particles of the spring, their' amplitudes of oscillation and distance from the spin axis are all reduced from the same parameters of conventional Centrifugal forces acting on the spring are practicallyproportional to the active length of the vibrating escapement spring. This length is reduced to. a minimum in the improved construction 3,1es,ssa

3 described. Thus it has been found that a timer or clock provided with a timing escapement mechanism embodying the invention will function accurately about a set time over a relatively wide spin range and is thus Well adapted for use in timing systems for modern high-speed artillery shells and the like.

The invention, will, however, be further understood from the following description, when considered with reference to the accompanying drawings showing certain embodiments thereof, and its scope is pointed out in the appended claims.

in the drawings:

FIG. 1 is a plan view of a timing escapement mechanism embodying the invention,

FIG. '2 is a side view, in elevation and partly in section, of the mechanism of FIG. 1, taken on the section line 2-2 thereof, to show certain constructional features in accordance with the invention,

PEG. 3 is a plan view of a portion of the mechanism of FIG. 1, showing a prior art modification thereof to illustrate certain features of the invention as improvements thereon,

MG. 4 is a view in perspective of a timing escapement mechanism embodying the invention as a modification of the mechanism shown in FIGS. 1 and 2,

FIG. 5 is a plan view of a portion of the mechanism of FIG. 4 showing more clearly a detail of construction in accordance with the invention, and

FIG. 6 is a sideview, in elevation, of a fuse for an artilleryor like projectile, showing the locations therein of a timed mechanism and timing escapement mechanism of the presentinvention as the time base control element thereof. i

' means provided in fixed supporting plates 28 and 29, as

viewed in FIG. 2. The axis of the arbor lies in the axis of movement 30 of the body or carrier which is the axis of spin in the present example, assuming the casing section 310 to be that of an artillery shell fuze, for use with which the invention is best adapted at present.

The oscillating or oscillatory mass is connected through the arbor with a pair of oppositely-disposed radiallyextending hairsprings or escapement springs 31 and 32 of the cantilever type. One spring alone could be used, but two provide symmetry in the balanced relation of parts with respect to the axis of spin 3t! and the pivot axis 25, which are coextensive and the same, as above noted, and each of the two springs may be relatively short, as is desirable.

The escapement springs are relatively thin fiat strips of metallic spring material, with the remote, radially-outer Referring to the drawings, wherein like elements throughout the various figures are designated by like reference numerals, and referring particularly to FIGS. 1 and 2, a cylindrical section iii of the outer casing or frame of a moving body adapted for travel in a fiight path or trajectory in space is provided witha hollow interior or chamber 11 in which is located a timing escapement mechanism 12 in accordance with the invention.

The mechanism comprises an escapement wheel 14 which ma as indicated, be of a conventional construction with a plurality of equal, spaced, radial escapement teeth 15 having sloping pallet-actuating end surfaces 16. The wheel is mounted to rotate on a pivot shaft 1'7 in connection with a pinion gear 18 which may form part of a gear train (not shown) connecting the wheel witha controlled timed mechanism such as a fuze timer, for example. The external connection between the escapement wheel pinion gear 13 and the timed mechanism is indicated by the dot and-dash line 19. This connection may include a source of energy for driving or biasing the wheel 14 to rotate in one direction as indicated by the arrowed. line adjacent thereto. As this source may be of any suitable form and be included in the timed mechanism, the same is not shown. Since the timed mechanism also is not part of the present invention, no further description is believed to be necessary.

A pivoted escapement lever 21, having two effectivelyradial and oppositely-disposed weight arms 22, is mounted,

together with two-bladed escapement means or pallets 23' and 24, to oscillate about the pivot axis 25 of an operating arbor 26. The pallets are positioned to control the stepby-step rotary movement of the escapement wheel 14 as they knife alternately in and out of the toothed periphery of the wheel. As is understood, the trailing pallet 24 receives a thrust from each tooth via the cam surface 15, thus keeping the lever and the pallets oscillating about the axis 25 from the energy received through the control and driving connection 19.

The arbor 26 and the lever 21, together with the pallets 23 and 24, are rigidly assembled to form the oscillating mass of the escapement mechanism 12. The arbor is pivotally mounted in upper and lower tapered bearing ends fixed in rigid mounting blocks or keepers 33, carried by the frame or casing section 10 of the body. The outer ends of the springs are thus anchored to the movement body. The springs extend radially inwardly toward and substantially to the pivot axis of the arbor and spin axis. The inner ends are connected to move laterally or vibrate as the arbor oscillates with the connected lever or oscillating mass. In the present example, as a presently preferred means for connecting such single-leaf springs with the oscillating arbor, the inner ends of the springs 31 and 32 engage individual slots or notches 34 and 35, respectively, on diametrically opposite sides of the arbor 26. The notches are constructed preferably, as indicated, to provide close knife-edge contact with opposite faces or sides of the escapement springs 31 and 32.

The active lengths of the escapement springs which oscillate with the arbor, from the positions of rest shown,

to the respective deflected positions 31' and 32 shown in FIG. l, are controlled by individual clamps or blocks 37 connected with the body and adjustable along the length of the springs. In the position of rest shown, the weight arms 22 are seated against stop blocks 38resiliently movable against spring cushioning means 39 as the arms come to rest on each oscillation. The blocks 38 are pivotally connected with the casing section or frame 10. The arms move in the directions'of the arrowed lines.

The escapement springs extend through and closely fit slots or grooves 40 of rectangular cross-section, in the blocks 37 and are thus firmly held or effectively clamped inthe radially outer and inactive portions. The blocks are positioned, guided and moved by suitable screws, such as. the screw 41 shown in FIG. 2, rotatab'ly connected with the frame through the fixed spring mounting blocks or keepers 33 and threaded into each block as indicated. Each screw is provided with a head 42 adapted for screw driver adjustment and rotatable in an opening 43 in the keeper 33 to cause the movable block 38 to travel along the spring 32 for, example, thereby to adjust the length of the free or active end thereof, and thus the timing or frequency rate of the mechanism; Where two springs are provided in opposite balanced relation, as in the present example, both are similarly adjusted to provide the desired overall timing or frequency rate.

' By this improved construction, the active or oscillatory length of each escapement spring is at the radially inner end and relatively close to the axis of spin. Furthermore the escapement spring length is considerably reduced, thus reducing the effective centrifugal and like forces that may act thereon. Compared with conventional escapement mechanisms of this type as outlined in FIG. 3, for example, the total mass of the working particles of the escapement spring, thev amplitude of oscillation of the particles, and their distance from'the spin axis are all greatly reduced in the construction according to the present invention.

Referring to FIG. 3, along with the preceding figures of. the drawing, the escapement lever 21, with its weight arms 22, is connected to oscillate with the arbor 26 and pallets (not shown) to control the stepping of the escapement wheel 14 at a desired frequency or timing rate as hereinbefore described. In this construction, however, the escapement spring, designated at 44, is one elongated flat strip, clamped at its center to the arbor 26 by suitable means such as a pin '45, and extending radially therefrom in opposite directions with two free ends 47. The latter pass through knife-edged guide slots in movable adjusting nuts or retainers 48 adapted to permit the spring to bend or flex on opposite sides of the arbor as indicated in dotted lines 49 in response to oscillations of the arbor and connected mass. 7

When such a spring structure and control are mounted in a spinning body or carrier, like a fuze on an artillery shell in motion, all parts of the spring are subjected to centrifugal forces acting in opposite directions on the two halves of the spring and introducing additional tensions which oppose the deformation or bending in a manner to cause the spring eifectively to increase in stiffness. This results in an increase in the frequency of the escapement mechanism and a corresponding shortening of the functioning time with respect to the setting time. In addition to the frequency increase, the stiffening effect on the conventional escapement spring tends to require a higher driving torque at the escapement wheel when the spin effect tends to reduce it. These adverse influences of the spin or movement can affect the accuracy of a timer in which such escapement mechanisms were used, and even stop the timer if the spin or movement is of sufiicient magnitude. 1

While in the conventional construction shown in FIG. 3, the hair spring or escapement spring 44 operates as a beam supported on its radially-outer ends 47 by the adjusting elements 48 and loaded by a moment at the center, in the improved construction of FIGS. 1 and 2, the springs 31 and 32 operate as cantilevers or cantilever beams anchored each at one end and clamped by the adjusting blocks 38, and further loaded on their free radially-inner ends with a force at the arbor operating substantially at a right angle thereto. Because of these basic differences in construction and operation, using substantially the same springs and With the escapements regulatedto the same frequency, the improved construction inaccordance with the invention shows the following advantages:

(1) The working length of the hair spring or escapement spring is approximately only one-third the length required by conventional springs. Hence there are fewer particles moving out of their neutral positions Where they can be adversely affected by the body spin or movement.

(2) For the same angular movement of the oscillating escapement lever, the amplitudes of the oscillating particles of the escapement spring or springs are very much smaller. l I

(3) The particles of the escapement spring or springs having the greatest amplitude of movement are those which are nearest to the axis of spin or movement of the carrier. q

(4) In the formula for centrifugal force (Fc) as applied to this construction, both the total mass (m) and the spinning radius (r) are reduced several times, and the resulting centrifugal force Fc=mrw (where w is the angular velocity of the spin), is reduced by the ratio:

mr' (conventional FIG.3 construction) mr (improved FIG. 1 and 2 construction) in which 2 may have a practical numerical value of at least 20 and often more, thus illustrating how much the being effective in the same direction, and thus aiding the accuracy of the timer in which the improved mechanism is used.

(6) Because the active or working length of the escapement spring is much shorter, it is possible to regulate the escapement mechanism for a large band of frequencies or wide timing range and thus obtain longer functioning time if desired, without modification of the'construction of any timer in use with the improved escapement mechanism of the present invention.

Further in accordance with the invention, a single radial cantilever beam construction may be provided for the escapement or hair spring without changing the principle of operation or losing any of the advantages above outlined. As hereinbefore pointed out, the construction shown in FIGS. 1 and 2, utilizes two spring elements to complete the balanced relation of operational parts which move about the axis of the arbor and the spin axis. One spring element could provide effective operation in accordance with the invention, as described.

A further modification of this type is shown in FIGS.

' -4 and 5, to which attention is now directed, along with the'preceding FIGS. 1 and 2. As in the preceding embodiment, the arbor 26is pivoted to oscillate about its axis 25 and the spin axis 30 of the moving body, and is rigidly connected to the escapement lever 21 wtih its two arms 22 and additional weights 52 attached thereto near the outer ends. The weights provide effective mass with greater moment arms in connection with the arms 22 which may then, as indicated, be of relatively-thin sheet material.

The pallets 23 and 24 are carried by the lever in connection with the arbor and operate to control the escapement wheel 14 with its radial teeth 15 and camming surfaces 16 for the pallets as hereinbefore described,

The wheel rotates on the pivot shaft 17 in connection with the pinion gear 18 which is connected, as indicated at 19, with the remainder of a gear train 53 having a driving connection with the timer mechanism or timer indicated at 54. The driving torque for the escapment wheel is applied through this connection from any suitable source, for example, as contained in the 'timed'mechanisr 54 for thepurposes hereinbefore described.

In the embodiment of FIGS. 1 and 2, the hair spring or escapement spring means for the mechanism comprised two flat spring leaves extending radially from the axis of the arbor and the diametrically-opposite sides thereof, with'the outer ends anchored or fixed in connection with the moving body or the carrier. In the present embodiment, the escapement spring means is a dual bladed or two part spring 55 of the same cantilever typemo'unted to extend radially from the arbor 26 to an anchor block 56 carried by the'body or outer casing of the section containing the escapement mechanism, as before described.

The spring 55 comprises two equal flat strips 57 and 58 extending in close contacting parallel relation through the anchor block 56, in which they are staked .tight, and

through a close fitting slot 60' in a movable clamp or block 61, to the arbor and a radial lug 62 thereon with which the strips are in contact on opposite sides, as shown more clearly in FIG. 5. A similar lug 63 is provided diametrically opposite tothe lug 62 whereby the system may be adapted for use with a, second dual-bladed or two-part spring in a balanced structure similar to that of FIGS. 1 and 2. However, the single-spring dual-bladed structure is atpresent preferred as being'highly-effective, compact and simplified inform. I

The arbor lug extends radially outwardly between the free radially-inner ends of the escapement spring strips or leaves. The spring ends are thus separated at their inner active ends, by the lug, and as the arbor 26 oscillates in operation, the spring ends serve alternately to drive the arbor and the lug toward the central neutral position of rest shown in FIGS.- .4 and 5. At least one spring leaf is e,1es,sss

in contact with the arbor lug at all times. As indicated in FIG. 4, the two spring leaves or strips 57 and 58 may be joined by a loop or hair-pin link 65 in a one-piece hairpin element of which the strips 57 and 58 are the legs.

As in the preceding embodiment, the block or clamp element 61 is movable along the dual-bladed spring element 55 to adjust the length of the active radially inner end thereof, which, in the present modification, comprises the dual-blade elements 57 and 58 gripping the driving or connecting lug 62 on the arbor. The operation is substantially the same as previously described but with a much simplified construction as is obvious from a comparison of the elements of FIG. 1 and FIG. 4, for example.

In a typical artillery shell fuze as indicated at 68 in FIG. 6, the timed mechanism 54 and gear train 53 may be located as shown and connected with the escapement mechanism 12 in the lower end, and this arrangement is one which has been found to be suitable for the equipment described. In other moving bodies or vehicles adapted for directed flight, otheriarrangements may be used as best adapted to keep the axis of the arbor in alignment with the major axis of movement or. rotation in any.

case.

From the foregoing description it will be seen that the timing escapernent mechanism of the present invention is constructed to provide substantial immunity from the efiects of spin or like movement on the liming action or frequency thereof. The escapernent or hair spring element is reduced in length and placed close to the spin axis, and radially extending from the arbor to the clamp which is rigid and readily adjustable. A substantially spin-insensitive escapement mechanism is'achieved by the improved construction as shown and described.

I claim: I

1. A timing escapement mechanism for mechanical timers and thelike adapted for movement about a predetermined axis in connection with a body in motion, comprising in combination, a frame element adapted to be carried by said body, an operating arbor pivoted in said frame element for oscillatory motion on an axisprovided for alignment with said axis of movement, a rotary timing escapement Wheel, means connected with said wheel transmitting rotational timing movement and control thereby externally of said mechanism, means providing a balanced escapement lever and pallet inconnection with the arbor for oscillation about said pivot axis to control the escapement wheel and. said'timing movement, an escapement spring ofthecantilever beam type having one end in mo tion-transmitting engagement with the arbor and extending radially therefrom to a fixed anchor point at its outer end in the frame element, and means movable along said spring between said outer end and the arbor in clamping engagement with an extended portion of its length for rigidly fixing the radially-outer end portion thereof and adjusting the length of the radially-inner free end portion of the spring for oscillation with the arbor at ditferent timing rates.

2. A timing escapement mechanism as defined in claim 1, wherein the spring is a flat strip of flexible spring material extending into a slot in the arbor having close knifeedge contact with Opposite faces-thereof, and wherein the length-adjusting means is an elongated sloted block of relatively large mass movable along the spring with a firm sliding fit in connection therewith.

3. A timing escapement mechanism as defined in claim 1, wherein the escapement spring comprises two fiat strips of spring material extending in close contacting parallel relation into connection with the arbor at the radiallyinner ends thereof, and wherein the engagement with the arbor is provided by a radial lug element thereon interposed between and gripped by said ends of the-spring strips,

whereby as the arbor oscillates in operation, at least one- 1, wherein a second escapement spring of the cantilever beam type has a free end in detachable driving engagement with the arbor and extends radially therefrom in substantially diametrically-opposite balanced relation to the first spring and is anchored at its radially outer end in said frame element, and wherein a second means movable in clamping engagement with the second spring are provided between the outer end thereof and the arbor for adjusting the length of the radially-inner free end in engagement with the arbor and cooperatively with the first spring and its adjustment for oscillation therewith at said different timing rates.

5. A. timing escapement mechanism for mechanical timers in projectilefuzes and like movement bodies having a relatively high'spin rate about one axis thereof, comprising in combination, a frame element having a predetermined spin axis in connection with a movement body of the type referred to and adapted to be mounted therein, an operating arbor pivotally mounted in said frame element for oscillation on said spin axis, timing escapement means including an escapement wheel having means connected therewith to provide transmission of controlled timing movement externally of said mechanism and balanced escapement lever and pallet means for said wheel mounted on said arbor for oscillation therewith, andan escapement spring of the flat cantilever type anchored and fixed at one end. to said frame element and extending therefrom radially inwardly withrespect to and into driving engagement with the arbor at the radially-inner end for vibratory movement therewith as the arbor oscillates, and said spring being therebyloaded at said radially inner end with a force at the arbor operating at a right angle thereto and substantially at the axis of spin, whereby timing 'control of said mechanism is substantially devoid of adverse effects from operational spin impartedto said frame element on said axis, and means movable along said spring in engagement therewith for clamping the, radially outerv portion of said spring and adjusting the length of the inner vibratory free end thereof in engagement with the arbor to set the timing rate of said mechanism.

6. A timing escapement mechanism as defined in claim 5, wherein the radially inner end of the escapement spring is connected with a slot in the arbor providing knife-edged contact therewith, and wherein the means for clamping and adjusting the spring includes an elongated movable block of relatively large mass having a longitudinal open slot for receiving and holding the spring against vibration and oscillatory movement between the free radially-inner end and the anchor point on the frame means.

7. A timing escapement mechanism as defined in claim 5, wherein theescapement. spring is of dual-bladed flatleaf construction with two flat strips in close contacting parallel relation through the clamping means and having two inner ends, and wherein the arbor has a radial lug extending between and gripped by said ends to provide the driving engagement therewith. Y

8. A timing escapement mechanism for use in a body adapted for travel in a trajectory or flight path in space and having an outer frame element and internal apparatus including a timer for the operation thereof, to provide a timing-control action on said timer in substantial independence of forces acting thereon and on said body in flight normally tending to adversely affect timing and control functions therein, said timing escapement mechanism comprising, an operating arbor pivoted for oscillatory movement in connection With said frame element on an axis adapted to be aligned with the major axis of movement of said body, a step-by-step rotary timing escapement wheel adapted to be connected with said timer and driven through said connection for rotation in one direction to control said timer, an escapement lever and two-bladed pallet element mounted on said arbor for oscillation about .said pivot axis to control the step-by-step rotary movement end in driving engagement with the arbor and extending a References Cited by the Examiner UNITED STATES PATENTS Whitehead 58117 Whitehead 58117 X Whitehead 58-117 X Reinhardt 74-15 De Gryse et a1. 58116 BROUGHTON G. DURHAM, Primary Examiner. MILTON KAUFMAN, Examiner. 

1. A TIMING ESCAPMENT MECHANISM FOR MECHANICAL TIMERS AND THE LIKE ADAPTED FOR MOVEMENT ABOUT A PREDETERMINED AXIS IN CONNECTION WITH A BODY IN MOTION, COMPRISING IN COMBINATION, A FRAME ELEMENT ADAPTED TO BE CARRIED BY SAID BODY, AN OPERATING ARBOR PIVOTED IN SAID FRAME ELEMENT FOR OSCILLATORY MOTION ON AN AXIS PROVIDED FOR ALIGNMENT WITH SAID AXIS OF MOVEMENT, A ROTARY TIMING ESCAPEMENT WHEEL, MEANS CONNECTED WITH SAID WHEEL TRANSMITTING ROTATIONAL TIMING MOVEMENT AND CONTROL THEREBY EXTERNALLY OF SAID MECHANISM, MEANS PROVIDING A BALANCED ESCAPEMENT LEVER AND PALLET IN CONNECTION WITH THE ARBOR FOR OSCILLATION ABOUT SAID PIVOT AXIS TO CONTROL THE ESCAPEMENT WHEEL AND SAID TIMING MOVEMENT, AN ESCAPEMENT SPRING OF THE CANTILEVER BEAM TYPE HAVING ONE END IN MOTION-TRANSMITTING ENGAGEMENT WITH THE ARBOR AND EXTENDING RADIALLY THEREFROM TO A FIXED ANCHOR POINT AT ITS OUTER END IN THE FRAME ELEMENT, AND MEANS MOVABLE ALONG SAID SPRING BETWEEN SAID OUTER END AND THE ARBOR IN CLAMPING ENGAGEMENT WITH AN EXTENDED PORTION OF ITS LENGTH FOR RIGIDLY FIXING THE RADIALLY-OUTER END PORTION THEREOF AND ADJUSTING THE LENGTH OF THE RADIALLY-INNER FREE END PORTION OF THE SPRING FOR OSCILLATION WITH THE ARBOR AT DIFFERENT TIMING RATES. 